The present invention relates to a method of manufacturing fine pattern, and a printed circuit board manufactured by using this method. In particular, the invention relates to a method of manufacturing fine pattern suitable for use as an etching mask and a plating mask in manufacturing a printed circuit board, and a printed circuit board manufactured by using the fine pattern. The fine pattern is used when manufacturing fine line and high density printed circuit boards, multi-layered printed circuit boards, flexible printed circuit boards and the like which are incorporated into semiconductor packaging such as IC cards, and electronic equipment such as portable information terminals.
The conventional method of manufacturing a print circuit board (hereinafter referred to as xe2x80x9cPCBxe2x80x9d) includes a subtracting method, in which circuit conductors are formed by making up a predetermined insulating pattern over a copper foil on a surface of a copper clad laminate, followed by removal of any unnecessary portion of the copper foil with an etching process. Another method of manufacturing a PCB, among others, is an additive method, in which circuit conductors are formed by applying a catalyzer over a surface of an insulation substrate, followed by formation of a predetermined insulating pattern, and an electroless copper plating.
On the other hand, photolithography is one method of forming an insulating fine pattern on a substrate surface, by applying a photosensitive resist on the substrate, exposing, and developing it. This method is used commonly in the method contains a complicated manufacturing process, since it requires an application and exposure of photosensitive resist for every layer of circuits. Also, the products manufactured by the photolithography method have been expensive, because various kinds of equipment are used. For example, necessary equipment for exposure of ultraviolet rays to the photoresist is expensive.
On the other hand, there are printing methods for forming a fine pattern directly on a substrate, as means of forming the insulating fine pattern in a shape of circuits on the substrate at lower cost. Although there are such printing methods as offset printing, screen printing, and the like methods, it is not feasible to form a pattern of 100 xcexcm or less in width with any of these methods in mass-production. In addition, the printing methods are not suitable for making a pattern of high definition, since they are not considered satisfiable in respect of reproducibility.
Therefore, the photolithography, which is superior in quality, even though it is more costly, has been utilized principally in order to satisfy a demand for PCB""s of thinner film, higher density and increased layers with the latest progress of semiconductors requiring higher operating frequencies, and electronic devices for downsizing and greater integration.
Under the situation as described, a new method has been desired for forming fine pattern with a simple process and economically low cost, while maintaining high quality. Several methods have been devised in attempting to improve preciseness while also obtaining a simplification and low cost in the manufacturing process of forming fine pattern. Some of the methods will be described hereinafter.
According to the teaching of Japanese Patent Laid-Open Publication, Number S63-266482, a method is suggested, in that a fine pattern film in high precision is formed first on a master substrate. A fine pattern film is then transferred onto another substrate. The above method of forming fine pattern is utilized for manufacturing a color filter. In the manufacturing, it uses an insulating master substrate having an electrode corresponding to a shape of the color filter on its surface. A fine pattern film made of resin is formed by electro-depositing the resin on the electrodes corresponding to each color of the master substrate. The fine pattern film is then tightly pressed onto another substrate, to exfoliate and transfer the fine pattern film onto the substrate by making full use of the electro-deposited resin""s own tackiness. This method is superior in economical standpoint, because the master substrate can be used repeatedly, thereby eliminating an exposure operation for each PCB during the process of forming the fine pattern film. However, the fine pattern film has a weak adhesion to the substrate being transferred, since the exfoliation and transference is made only by the electro-deposited resin""s own tackiness. At the same time, it has a shortcoming in that a full transference cannot be made reliably due to a strong adhesion of the fine pattern film to the master substrate.
Also, there is a kind of master substrate for forming fine pattern, as disclosed in Japanese Patent Laid-Open Publication, Number H06-301198, as an example. It discloses a method in which a layer of photo-resist in a shape of fine pattern is formed on a thermally oxidizable metal plate such as stainless steel, titanium and tantalum, or a nitridable metal plate such as titanium and silicon. An insulating pattern-masking layer composed of oxide film or nitride film is then formed by thermally oxidizing or nitriding a portion not covered by the layer of photo-resist. The metal plate produced in the above step is used as a master substrate for forming the fine pattern. The insulating pattern-masking layer has a strong adhesion to the master substrate, since the insulating pattern-masking layer is produced from the thermally oxidizable metal plate or the nitridable metal plate. There have been problems even with this master substrate, such as deterioration of a fine pattern film, low in yield, and a short usable life of the master substrate. The fine pattern film needs to be separated forcedly in order to totally exfoliate and transfer the film due to the strong adhesion of the film to the master substrate.
On the other hand, the inventors of this application have devised and disclosed in Japanese Patent Laid-Open Publication, Number H09-272345, a method of manufacturing fine pattern, which weakens adhesion of a fine pattern film made of electro-deposited resin to a master substrate, thereby enabling complete exfoliation and transference of the film. The method disclosed by the inventors uses a master substrate having a pattern electrode layer in a predetermined shape on the substrate, and an exfoliation layer composed of a thin water repellent film formed on the master substrate. Furthermore, a fine pattern film is formed on the master substrate by electro-depositing, and the film is hydrated with hot water in temperature of not less than 40xc2x0 C. but not more than 90xc2x0 C. The hydration, i.e. impregnation of water, of the fine pattern film can weaken adhesion due to water repellency of the exfoliation layer on a surface of the master substrate. In addition, a surface of the fine pattern film is warmed so as to turn it into a state of tackiness. Therefore, the above method is able to exfoliate and transfer the fine pattern film completely onto a substrate subject to be transferred.
The method of forming fine pattern, as described above, is to form a fine pattern film on a master substrate with electro-depositing, and to exfoliate and transfer the film onto a substrate subject to be transferred. This method is able to form the fine pattern film of high quality, if the master substrate is precisely made. The method is also capable of producing the fine pattern film easily at low cost with quite a simple process, since it does not require use of photolithography for each of every formation of the fine pattern, and it can allow repeated use of the same master substrate.
However, there are two types of electro-depositing, anion type and cation type depending on electric charge of the ionic radical introduced into an electro-deposited resin. In the case of utilizing an electro-deposited film for forming a fine pattern as disclosed in the above-cited invention, an anion type electro-deposition is suitable in order to avoid mingling gas bubbles in the electro-deposited film, since the anion type does not generate many gas bubbles during the process of the electro-deposition. However, the anion type electro-deposition causes deposition of the electro-deposited film in a positive electrode, resulting in an erosion of the electrode as a side reaction caused by electrolysis of water. As a result, the pattern electrode layer on the master substrate deteriorates causing shortening usable life for the master substrate.
Also, Japanese Patent Laid-Open Publication, Number H03-150376 discloses an adoption of a master substrate, in which a photo-resist layer in negative form corresponded to a fine pattern is formed on an electrically conductive substrate. This method electro-deposits a film of pattern on a portion of the master substrate not covered by the photo-resist layer with electro-deposition, and exfoliates and transfers the film on a substrate subject to be transferred with a pressure sensitive or a conventional adhesive, in order to obtain fine pattern. Even with these master substrates, the fine pattern film needs to be separated forcibly, since the fine pattern has a strong adhesion to the electrically conductive substrate. Hence, a problem still exists where a yield of products is unsatisfactory due to damages, etc. of the fine pattern. It also has a short life for repeated use due to damages to the master substrate because of the forced separation. The cited publication also discloses another method for making a master substrate by forming a pattern electrode on an electrically conductive substrate with pattern-etching. An insulating resin is placed in a recessed portion on the etched substrate. And a fine pattern, which is formed on a surface of the pattern electrode with electro-deposition, is exfoliated and transferred onto a substrate subject to be transferred. However, this method still has a problem as the preciseness is less satisfactory when compared with a fine pattern formed with the photo-resist layer, although the master substrate can be manufactured at low cost with the pattern-etching.
An object of the present invention is to deal with the foregoing problems of the prior art, and aims at disclosing a method of manufacturing fine pattern, which reliably provides mass-produced films of fine pattern in fine line and high density at low cost, with use of a master substrate having a superior transferability and durability, as well as high pattern accuracy.
Another object of the present invention is to provide a fine-line and high-density PCB manufactured using above method at low cost.
A method of manufacturing fine pattern of the present invention comprises the steps of:
(a) a master substrate manufacturing step for producing a master substrate, a surface of which is provided with at least an insoluble electrode film made of precious metal such as gold and platinum, or their alloy;
(b) a fine pattern formation step for forming a fine pattern film on the insoluble electrode film with an anion type electro-deposition; and
(c) an exfoliation-and-transferring step for transferring the fine pattern film formed on the master substrate onto a substrate subject to be transferred by adhering the fine pattern film onto the substrate, and exfoliating it from the master substrate. In the foregoing structure where the insoluble electrode film is provided on the master substrate, an erosion of the electrode due to the anion type electro-deposition is avoided. As a result, this method realizes use of the anion type electro-deposition that generates only a small amount of gas bubbles, so as to produce the fine pattern with high yield.
Also, a second method of manufacturing fine pattern of the present invention comprises the steps of:
(a) a master substrate manufacturing step for producing a master substrate, a surface of which is provided with at least a sacrificial electrode layer that is reproducible repeatedly with plating;
(b) a fine pattern formation step for forming a fine pattern film on the sacrificial electrode film with an anion type electro-deposition; and
(c) an exfoliation and transferring step for transferring the fine pattern film formed on the master substrate onto a substrate subject to be transferred by adhering the fine pattern film onto the substrate, and exfoliating it from the master substrate. This method provides for the sacrificial electrode layer on the master substrate, and thereby the electrode layer can be readily reproduced repeatedly even if the anion type electro-deposition causes erosion of the electrode.
Furthermore, a third method of manufacturing fine pattern of the present invention comprises the steps of:
(a) a first step for producing a master substrate by forming an electrically conductive pattern electrode on an electrically conductive substrate with electro-forming, and exfoliating and transferring the pattern electrode, whereby an exfoliated surface of the transferred pattern electrode is exposed;
(b) a second step for forming a film of pattern with electro-deposition on an exfoliated surface of the pattern electrode transferred onto the master substrate; and
(c) a third step for transferring the film of pattern on a substrate subject to be transferred. The foregoing method improves a transferring ability of the master substrate and accuracy of the film of pattern, thereby exfoliation and transferring of the film can realize mass-production of fine pattern of fine line and high density with high quality and high yield.